Lightning protection means for a wind turbine

ABSTRACT

A lightning protection device which is capable of avoiding electrical current, which is being induced in the blades of wind turbine, from being passed to parts of the wind turbine that may be damaged or destroyed by the electrical current. The electrical current is passed along by electrical conductors extending from the blades to a stationary part of the wind turbine. A flange for mounting the hub of the wind turbine to the main shaft is provided where the electrical conductors lead either through or past the mounting flange.

FIELD OF THE INVENTION

The present invention relates to a wind turbine with lightningprotection means, said means comprising means for conducting anelectrical current induced by a lightning, said means capable ofconducting the electrical current from blades of the wind turbine and tothe nacelle of the wind turbine, through the hub and to a stationarypart of the wind turbine by leading the electric conductor means past aflange for mounting the hub to a main shaft of the wind turbine, saidstationary part of the wind turbine being stationary in relation to themounting flange during operation of the wind turbine.

BACKGROUND OF THE INVENTION

Different kinds of means are known for protecting electrically fragileparts of wind turbines from lightning. One kind of means is intended foravoiding the electrical current from a lightning striking the blades ofthe wind turbine from entering the generator and other electrical andelectronic components situated in the top of the wind turbine. This isdone by conducting the electrical current from the blades to the towerof the wind turbine and to the ground.

WO 01/86144 describes a wind turbine with such a lightning protectionsystem. The lightning protection system comprises a rod mounted to theblades of the wind turbine. The stick is mounted at the base of theblades. The rod is intended as lightning conducting means conducting thelightning from the base of the blades to a conducting ring mountedco-axially around the main shaft, outside the housing of the nacelle.From this conducting ring the electrical current is conducted throughthe machine carrying elements provided in the nacelle and further on tothe tower along a slip means provided at the yawing gear. Thereby, theconducting of the electrical current is independent of the actual rotaryposition of the machine carrying elements in the nacelle compared to thetower.

The apparatus described in the above WO-publication is said to becapable of ensuring that no electrical current from the lightningdamages the electrical and electronic components. However, the inventionis not so described as to enable the person skilled in the art to obtainthis object. Also, the means by which the lightning protection isprovided has disadvantages. Firstly, providing a separate conductingring outside and around the entire nacelle demands a very large ring andwhen mounted, though very difficult, inflicting the aerodynamicproperties of the wind turbine nacelle. Also, how the large conductingring is suspended in relation to the machine carrying elements of thenacelle is not described. Accordingly, the mounting of the conductingring, which, as mentioned, is one of the major disadvantages of theapparatus, is not mentioned. Therefore, the person skilled in the artwill not only be posed to the disadvantages apparent from thedescription, i.e. the large conducting ring, but will also have to applya very inventive skill in order to overcome the problem of how to mountthe large conducting ring.

DE 197 48 716 describes a lightning protection system comprising atleast two conductors inside the turbine blade. The one conductor leadsto one side of a transformer, said transformer being capable ofgenerating electrical current in the conductor for heating the blade.However, the one conductor also functions as lightning conductor. Inthis case, the conductor is connected either directly to the hub asshown in FIG. 1, or to a separate ring provided around the main axle andoutside the nacelle of the wind turbine as shown in FIG. 2, or to aseparate lightning rod as shown in FIG. 3 and situated outside thenacelle and conducting the lightning voltage to any metal part in thevicinity of the lightning rod.

EP 0 718 495 describes a lightning conductor very like the one shown anddescribed in WO 01/86144. Thus, a separate conductor ring is providedaround the main shaft outside the nacelle. A conductor plate, alsoprovided outside the nacelle conducts the lightning form the separateconductor ring to the tower of the wind turbine and therefrom to theground. The lightning voltage is passed from the turbine blade via aspark gap to the separate conductor ring, from the separate conductorring via a spark gap to the separate conductor plate and from theseparate conductor plate via a spark gap to the tower.

EP 1 154 537 describes a lightning conductor comprising a slip ringprovided around the main shaft and brushes passing lightning voltagefrom the slip ring to a fixed structure secured to the body of the windturbine. The fixed structure serves as a protection shield for thegenerator of the wind turbine. The lightning voltage is passed fromlightning conductors in the blade along an exteriorly placed cable tothe slip ring, and from the slip ring to brushes and the protectionshield being part of the fixed structure of the turbine.

It is the object of the present invention to provide a lightningprotection means for a wind turbine, said means providing the necessaryprotection of the electrical and electronic components of the windturbine, and being easy to install, both in the sense of thecraftsman-like skills necessary, and also in sense of the number of andthe type of components used, seeing that the lightning protection meansis to be installed and serviced in the nacelle of the wind turbine, highabove ground level or sea level.

SUMMARY OF THE INVENTION

This object is obtained by wind turbine lightning protection means,where leading of the electrically conducting means past the mountingflange is established by one of the following means: Fastening meansprovided in or attached to the circumference of the mounting flange forfastening the electrically conducting means to the circumference of themounting flange, or through-going holes in the mounting flange forpassing the electrically conducting means through the mounting flange.

By leading the electrical current along the electrical conductor throughthe hub, all of the lightning protection system will be kept within theboundaries of the hub, thus neither necessitating specially adaptedmeans for suspending the lightning protection means to the hub or thenacelle, nor obstructing or impeding the aerodynamic properties of thewind turbine. However, passing the electrical conductors through the hubincur problems when having to pass the electrical conductors from thehub to the tower. This is accomplished by passing the electricalconductors either past the circumference of the mounting flange of thehub or by passing the electrical conductors through holes in themounting flange. Thereby, all of the lightning protection system will bekept within the boundaries of the nacelle as well, thus also assistingin not obstructing or impeding the aerodynamic properties of the windturbine.

Passing the electrical current from the mounting flange to the nacellemay take place in any suitable manner. However, due to the fact that themounting flange is rotating along with the main shaft and the hub, whenthe wind turbine is functioning, the present invention, in a preferredembodiment, makes use of special provisions for passing the electricalcurrent from the mounting flange to a stationary part of the windturbine.

In a first embodiment, the electrically conducting member comprises anannular member provided around the main shaft of the wind turbine, andsaid annular member being electrically insulated from the mountingflange and from the main shaft, and where the annular member is attachedto the mounting flange, thus rotating with the mounting flange, the mainshaft and the hub during operation of the wind turbine, and where slipmeans are provided between the annular member and the stationary part ofthe wind turbine, said slip means conducting the electrical current fromthe annular member to the stationary part.

In a second embodiment, the electrically conducting member comprises anannular member provided around the main shaft of the wind turbine, andsaid annular member being electrically insulated from the mountingflange and from the main shaft, and where the annular member is attachedto the stationary part of the wind turbine, thus not rotating with themounting flange, the main shaft and the hub during operation of the windturbine, and where slip means are provided between the annular memberand the mounting flange, said slip means conducting the electricalcurrent from the mounting flange to the annular member.

In principle, there is no difference in the individual parts and thefunction of the first embodiment and the second embodiment for passingthe electrical current from the mounting flange to the tower via astationary part of the wind turbine in relation to the mounting flange.The only difference is, whether the annular member is attached to themounting flange and thus rotates along with the flange during operationof the wind turbine, with the lightning current receptors beingstationary, or whether the annular member in stead is mounted to thestationary part of the wind turbine in relation to the mounting flangeand thus the lightning current receptors being attached to and rotatingalong with the mounting flange during operation of the wind turbine.

The slip between the lightning current receptors and the annular membermay also be accomplished in different ways. By slip is meant slip in itsbroadest understanding, i.e. not in the strict electrical understanding,the slip means thus being means allowing a mutual displacement betweenthe annular member and the stationary part, but still being capable ofconducting the electrical current induced by a lightning striking one ormore of the blades of the wind turbine and being passed to the slipmeans.

One embodiment according to the invention makes use of metal brushesconstituting the tip of the lightning current receptors. A secondembodiment makes use of carbon brushes constituting the tip of thelightning current receptors, such as frequently used in electricalgenerators and electrical motors. A third and preferred embodiment makesuse of a small gap between a pointed tip of the lightning currentreceptors and the annular member, thus creating a spark, when thecurrent is led from the mounting flange to the stationary part.

An overall object of the different possible embodiments according to theinvention for conducting the electrical current from the blades of thewind turbine to the stationary part in relation to the mounting flangeis to avoid electrical current being passed through sensitive parts andcomponents in the nacelle and possible other parts of the wind turbine.Thus, it is important to assure that parts such as bearings andcomponents such as the generator will not be affected by the electricalcurrent induced by the lightning and being passed to the stationary partin relation to the mounting flange. A stationary part in relation to themounting flange may be any part of the wind turbine apart from theblades, the hub and the main shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, where

FIG. 1 is a perspective view of an embodiment of the lightningprotection means according to the invention, also with other parts thewind turbine shown,

FIG. 2 is a perspective view of the embodiment viewed from the side andshowing the pathway for the current when passing from the hub to thetower, and

FIG. 3 is a perspective view of the embodiment viewed from the behind,also showing the pathway for the current when passing from the hub tothe tower

FIG. 4 is a perspective view of another embodiment of the lightningprotection means according to the invention, also with other parts thewind turbine shown,

FIG. 5 is a cross-sectional and perspective view of parts of the otherembodiment of the lightning protection means according to the invention,

FIG. 6 is a perspective view of parts of the other embodiment of thelightning protection means according to the invention, also with otherparts the wind turbine shown,

FIG. 7 is a perspective view of static discharge unit provided inaddition to and as a supplement to the lightning protection meansaccording to the invention,

FIG. 8 is a perspective view of a possible embodiment of a lightningcurrent receptor constituting part of the lightning protection systemaccording to the invention

FIG. 9 is a perspective view of a possible other embodiment of alightning current receptor constituting part of the lightning protectionsystem according to the invention

FIG. 10 is a perspective view of a possible yet other embodiment of alightning current receptor constituting part of the lightning protectionsystem according to the invention

FIG. 11 is a cross-sectional view of the possible yet other embodimentof a lightning current receptor constituting part of the lightningprotection system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a view showing parts of a wind turbine with lightningprotection means being installed. The parts of the wind turbine are anacelle 1 being in connection with a tower (not shown) of the windturbine, a main shaft 2, a front bearing 3 for the main shaft, and amounting flange 4 constituting a part of the main shaft, and formounting a hub (not shown) to the front end of the main shaft. Thebearing 3 is secured to the nacelle 1.

The lightning protection means comprises electrical conductors 5intended for passing inside the shelf of the hub, insulating sleeves 6intended for passing the electrical conductors through specially adaptedholes 7 (see FIG. 2) in the mounting flange and an annular member 8 (seeFIG. 2) being attached to the mounting flange by means of bushings 9(see FIG. 2) and intended for rotating with the mounting flange when thewind turbine is functioning.

Thus, the electrical conductors lead from the base of the blades (notshown) of the wind turbine, into the hub (not shown) into the speciallyprovided holes 7 in the mounting flange and to the annular member 8attached to the opposite side of the mounting flange, namely the rearside of the mounting flange, compared to the front side of the mountingflange, onto which front side the hub is mounted by means of themounting holes shown provided in the outer vicinity of the circumferenceof the mounting flange.

In an alternative embodiment, the electrical conductors do not passthrough holes in the mounting flange, but pass the circumference of themounting flange so that specially provided holes need not be provided inthe mounting flange. In an embodiment like this, notches may be formedin the circumference of the mounting flange, or even easier, clamps maybe attached to the mounting flange, said clamps fastening cables orother electrically conducting means to the circumference of the mountingflange.

FIG. 2 and FIG. 3 are close-up views seen substantially from the sideand seen from the rear, respectively, of how the lightning protectionmeans is placed in relation to each other and in relation to the partsof the wind turbine. As mentioned above, the electrical conductors 5pass from the hub (not shown) through the specially provided holes 7 inthe mounting flange 4. As mentioned, electrically insulating sleeves(see FIG. 1) are provided in the holes 7 for electrically insulating theelectrical conductors 5 from the mounting flange 4. However, if theelectrical conductors themselves are provided with insulation thickenough, the electrically insulating sleeves may be omitted.

In the embodiment shown, three electrical conductors are shown, one fromeach blade of a conventional wind turbine, and three corresponding holesare provided in the mounting flange. However, wind turbines havinganother number of blades may be provided with another number than threeelectrical conductors and corresponding holes. However, wind turbineshaving three blades may nevertheless have all three blades connected toone and the same conductor passing though only one hole in the mountingflange.

When the electrical conductors 5 have passed the mounting flange 4through the holes 7, the electrical conductors are passed to the annularmember 8. The annular member is electrically insulated from the mountingflange by being attached to the mounting flange using electricallyinsulating bushings 9 establishing a certain axial distance between themounting flange and the annular member. Opposing the annular member, anumber of lightning current receptors 10 are provided.

The lightning current receptors 10 are mounted in a ring 11 beingelectrically in contact with the basis of the tower, i.e. the ground ofthe sea, either along the tower itself or along wires leading throughthe tower to the basis. The electrical contact may be provided throughthe bearing 3 for the main shaft 2, or it may be provided separate fromthe bearing. The number of lightning current receptors is arbitrary. Thelightning current receptors have a pointed tip, and a small gap (notshown) is provided between the pointed tip of the lightning currentreceptors and the annular member. The size of the gab depends on thenumber of lightning current receptors and depends on the size ofelectrical current, which is expected during lightning, or which isintended for being conducted from the blades of the wind turbine and tothe ground or sea. Preferably the size of the gab is between 1 mm and 10mm, more preferably between 1 mm and 5 mm.

In alternative embodiments, the current is passed from the annularmember to the lightning current receptors by means of metal brushes orcarbon brushes constituting the tips of the lightning current receptorsin stead of the pointed tip and abutting the annular member, thuspassing the electrical current form the annular member to the lightningcurrent receptors without creating a spark.

FIGS. 4-7 are different views of another possible embodiment of alightning protection system. FIG. 4 shows from the rear side 4B of themounting flange 4 the main shaft 2 of the wind turbine together with thefront bearing 3 of the main shaft. The mounting flange 4 of the mainshaft is shown with a plurality of holes for mounting the hub (notshown) of the wind turbine to the main shaft 2. Electrical conductingcables 5 lead from the hub (not shown) to insulating sleeves 6 withfurther electrical conductors inserted into specially adapted holes 7(not shown) in the mounting flange 4. After having been passed troughthe mounting flange 4, the electrical conductors 5 are being led to theannular member 8.

FIG. 5 shows in greater detail and in a cross-sectional view the leadingof the electrical conductors 5 through the mounting flange 4 and to theannular member 8. An electrically insulated cable 5 such as a standardcable gland PG29 with amour earth ring and metric wire is situated inthe hub and lead from one of the blades mounted to the hub. Asmentioned, a specially adapted hole 7 is provided in the mounting flange4. Through the hole 7, a standard APE constituting the insulating sleeve6 is passed through the hole 7 to the annular member 8. The cable 5 isattached to a proximate end 6A of the APE by means of a cable plug 12.The annular member 8 is attached to a distant end 6B of the APE by meansof small bolts 13. In a possible embodiment as shown, the bolts 13 havebolt heads being flush with or at least not extending beyond the surface8B of the annular member facing lightning current receptors (see FIGS.8-11). The annular member 8 is secured to a rear side of the mountingflange 4 by means of electrically insulating insulators 9.

The electrically insulating insulators 9 are standard insulators beingprovided with threaded bolts in one end (see FIG. 7), and around thebody of the insulator means for rotating the insulator is provided, suchas a six-edged circumference 14 as shown for rotating the insulators bymeans of a wrench. When rotating the insulator the threaded end (seeFIG. 7) in the one end of the insulator is screwed into a correspondingthreaded hole (not shown) in the rear side of the mounting flange. Athreaded hole in the other end of the insulator is used foraccommodating a correspondingly threaded bolt screwed into the threadedhole (not shown) through a hole (not shown) in the annular member 4.

Alternatively, the insulator 9 may be provided with threaded bolts inboth ends, and the annular member being provided with a correspondinglythreaded hole. Rotation of the insulator 9 will thus result in each ofthe threaded bolts being screwed into the corresponding threaded holesin the mounting flange and in the annular member, respectively. By anyof the two attachment possibilities mentioned, an easy and secureattachment of the annular member to the rear side of the mounting flangeis obtained. If the annular member were to be attached to the bearing instead, similar attachment as the ones described above could easily beadopted.

FIG. 6 shows a different view than the view shown in FIG. 4, namely thelightning protection system seen from the front side 4A of the mountingflange 4. For the sake of clarity, the mounting flange 4 is however notshown. Also the main shaft 2 is not shown, but the front bearing 3 ofthe main shaft is shown.

As can be viewed, the embodiment comprises the electrical conductors 5such as cables, one for each of the blades of a preferred wind turbine.However, it will be possible to apply more electrical conductors thanonly one for each blade, and it will be possible to apply the lightningprotection system with wind turbines having another number of bladessuch as one blade, two blades or more than three blades. Finally, itwill be possible to connect the electrical conductors from each blade toone common conductor inside the hub, and just pass the one conductor tothe mounting flange and further on to the annular member.

The annular member 4 extends along an entire circular circumference. Itwill be possible, although not preferable, to divide the annular memberinto a plurality of sections, perhaps three sections, one section foreach electrical conductor. If only one of the blades during lightning isstruck by a lightning, only the electric conductor from that blade andthus only the section of the annular member, onto which that electricalconductor is attached, will pass the electrical current to thestationary part. The other sections of the annular member will notparticipate in the conducting of the electrical current from the oneblade.

FIG. 7 shows a possible embodiment of a unit 15 capable of dischargingany static electricity that may be formed between the annular member 8and the stationary part of the nacelle, onto which the electricalcurrent is passed from the annular member 8. In the embodiment shown,the electrical current is passed from the annular member 8 to a frontcover plate of the front bearing 3 of the main shaft. Accordingly, thestatic discharge unit is mounted to the front cover plate. The staticdischarge unit 15 consists in a brush mounted to the front plate of thebearing through electrically insulating insulators 9, the proximate endof which holds the discharge brush 15 by means of bolts or nuts and thedistant end of which is secured to the front plate of the bearing.

A threaded bolt 16 is shown extending from the one end of the insulator9, and the function of which is described with reference to FIG. 5. Inthe embodiment shown (see FIG. 6) only one static discharge unit 15 isprovided. However, it will be possible to provide more than one staticdischarge unit 15, and it will be possible to provide the one or morestatic discharge units 15 to other elements in the nacelle than thefront plate of the front bearing of the main shaft. Alternatively to thestatic discharge unit shown in FIG. 5, a resistor could be provided overthe insulator attaching the annular member to the mounting flange.

FIGS. 8-11 show different embodiments of the so-called lightning currentreceptors 10. The lightning current receptors are intended forestablishing the slip connection between the annular member 4 and thefront bearing of the main shaft, the stationary part inside the nacelle,which the current, in the embodiment shown, initially is passed on to.

FIG. 8 shows a first embodiment of a lightning current receptor 10similar to the lightning current receptors shown in FIGS. 1-3. Thelightning current receptor consists in a base 17 and a pointed tip 18,said pointed pin directed towards the annular member 4. The base 17 isby means of a bolt 19 secured to the front bearing 3 of the main shaft.A gap is providing a distance between the annular member 4 and the verypoint of the pointed tip 18.

When electrical current is established from a lightning striking one ormore of the blades of the wind turbine, the current is conducted to theannular member. A spark will be formed between the annular member andone or more of the tips of the pointed pins of the lightning currentreceptor. From the lightning current receptors, the current will bepassed further on along the front bearing of the main shaft tostationary parts of the wind turbine, such as the tower and further downthe tower to the ground.

FIG. 9 shows a second embodiment of a lightning current receptor alittle different than the lightning current receptors shown in FIGS.1-3. The lightning current receptor consists in plate member 20 having atip consisting in pointed prongs 21, said pointed prongs 21 directedtowards the annular member 4. The plate member is by means of a bolt 19secured to the front bearing 3 of the main shaft. A gap is providing adistance between the annular member 4 and the pointed prongs 21. Theplate member is bent in such a manner that the radial distance betweenan inner circumference of the annular member and the prongs of thelightning current receptor is smaller than an axial distance between thesurface 4B of the annular member 4, and facing the bearing 3, and theprongs 21 of the lightning current receptor.

When electrical current is established from a lightning striking one ormore of the blades of the wind turbine, the current is conducted to theannular member. A spark will be formed between the inner circumferenceof the annular member and the pointed tips of one or more of the platemembers constituting the lightning current receptor. From the lightningcurrent receptors, the current will be passed further on along the frontbearing of the main shaft to stationary parts of the wind turbine, suchas the tower and further down the tower to the ground.

FIG. 10 shows a second embodiment of a lightning current receptor alittle different than the lightning current receptors shown in FIGS.1-3. The lightning current receptor consists in plate member 20 having atip constituted by pointed prongs 21, said pointed prongs 21 directedtowards the annular member 4. The plate member 20 is by means of a bolt19 secured to the front bearing 3 of the main shaft. A gap is providinga distance between the annular member 4 and the pointed prongs 21. Theplate member is not bent, as is the plate member of the lightningcurrent receptor shown in FIG. 9, but is directed straight towards theannular member. Thus, the distance between the annular member and theprongs of the lightning current receptor is the axial distance betweenthe surface 4B of the annular member, facing the bearing 3, and theprongs 21 of the lightning current receptor.

When electrical current is established from a lightning striking one ormore of the blades of the wind turbine, the current is conducted to theannular member. A spark will be formed between the surface of annularmember and the pointed tips of one or more of the plate membersconstituting the lightning current receptor. From the lightning currentreceptors, the current will be passed further on along the front bearingof the main shaft to stationary parts of the wind turbine, such as thetower and further down the tower to the ground.

Alternative embodiments to the ones shown in FIGS. 8-10 may be thefollowing: The pointed tips of the lightning current receptors need notbe pointed tips but may instead be tips with no pointed shape, such ascylindrically shaped tips. The lightning current receptors need notconstitute single separate members in relation to the number oflightning current receptors. The pointed or non-pointed tips of thereceptors may be constituted by a ring encircling the front plate of thebearing, said ring being provided with tips at selected positions alongthe circumference of the ring, and said tips extending axially from thering towards the annular member. The gap established between the annularmember an the pointed or non-pointed tips of the lightning currentreceptors may be established along the outer circumference of theannular member as an alternative to along the inner circumference oralong the surface facing the receptors.

FIG. 11 is a cross-sectional view of the embodiment shown in FIG. 10.The electric cable is received from the hub of the wind turbine andattached by means of cable plug to the insulating sleeves such as an APEhaving a core for conducting electrical current. The electricallyinsulating sleeve is supported in a hole provided in the mounting flangefor mounting the hub to the main shaft of the wind turbine. Theinsulating sleeve with the conducting core is attached to the annularmember. The annular member is secured to a rear side of the mountingflange by means of electrically insulating insulators.

During operation of the wind turbine, the mounting flange together withthe main shaft will rotate. Thus, also the electric cables, theinsulating sleeves with the conducting core, the annular member and theinsulators attaching the annular member to the rear side of the mountingflange will all rotate together with the mounting flange, the mainshaft, the hub of the wind turbine and the blades of the wind turbine.

During operation, the front bearing of the main shaft will however notrotate. Accordingly, the lightning current receptors, which are securedto the bearing, will not rotate, either. Therefore the gap between theannular member and the pointed tips or tips of the lightning currentreceptors is established. By adjusting the position of the lightningcurrent receptors it will be possible to adjust the magnitude of thegap, i.e. the distance between the annular member and the tips or tipsof the lightning current receptors. By adjusting said distance, it ispossible to adjust at which potential difference a spark will be formedin the gap between the annular member and the tips or tips of thelightning current receptors.

Generally speaking, during lightning, the blades of the wind turbine maybe struck by a lightning. The blades are provided with electricalconductors of commonly known type running along the lengths of theblades. The electrical conductors of the blades run to the base of theblades and the electrical current is passed to the electrical conductorsconstituting part of the present invention. The electrical current isthen passed along the electrical conductors of the invention from thebase of the blade inside the hub, through the mounting flange and to theannular member.

When the electrical current reaches the annular member, the electricalcurrents pass on to the tips of the lightning current receptors bytraversing the small gab as a spark running from the annular member tothe tip of one or more lightning current receptors. From the lightningcurrent receptors the electrical current is passed to the ground eitherthrough the bearing and perhaps through the metal of the tower, orthrough specially adapted means (not shown) for leading the current fromthe lightning current receptors to the ground, perhaps along wiressuspended in the tower.

In an alternative embodiment, in stead of the annular member beingattached to the mounting flange and the lightning current receptorsbeing secured to the stationary part in relation to the mounting flange,the lightning current receptors may be attached to the mounting plateand the annular member secured to the stationary part. Thus, in stead ofthe annular member rotating with the mounting flange, the lightningcurrent receptors will be rotating with the mounting flange. However,the function of the lightning current receptors and the annular memberwill be exactly the same, also if the lightning current receptors areprovided with metal brushes or carbon brushes at the tips in stead ofbeing pointed for creating a spark gap.

1. A wind turbine lightning protection means, said means comprisingmeans for conducting an electrical current induced by a lightning, saidmeans capable of conducting the electrical current from blades of thewind turbine, and said means comprising electrical conductor meanspassing along the base of the blades, through the hub and to astationary part of the wind turbine by leading the electric conductormeans past a flange for mounting the hub to a main shaft of the windturbine, said stationary part of the wind turbine being stationary inrelation to the mounting flange during operation of the wind turbine,and where leading of the electrically conducting means past the mountingflange is established by one of the following means: fastening meansprovided in or attached to the circumference of the mounting flange forfastening the electrically conducting means to the circumference of themounting flange, or through-going holes in the mounting flange forpassing the electrically conducting means through the mounting flange.2. A wind turbine lightning protection system according to claim 1, saidelectrical conductor means leading past the mounting flange electricallyinsulated from the mounting flange.
 3. A wind turbine lightningprotection means according to claim 1, where leading of the electricalconductor means past the mounting flange are provided by leading theelectrical conductor means past the circumference of the mountingflange.
 4. A wind turbine lightning protection system according to claim3, where electrical insulation is provided between the electricalconductor means and the circumference of the mounting flange.
 5. A windturbine lightning protection means according to claim 1, where leadingof the electrical conductor means past the mounting flange are providedby leading the electrical conductor means through the mounting flange.6. A wind turbine lightning protection system according to claim 5,where electrical insulation is provided between the electrical conductormeans and holes in the mounting flange.
 7. A wind turbine lightningprotection means according to claim 1, where the electrical conductormeans comprises an annular member provided around the main shaft of thewind turbine, and said annular member being electrically insulated fromthe mounting flange and from the main shaft.
 8. A wind turbine lightningprotection means according to claim 7, where the annular member isattached to the mounting flange, thus rotating with the mounting flange,the main shaft and the hub during operation of the wind turbine, andwhere slip means are provided between the annular member and thestationary part of the wind turbine, said slip means conducting theelectrical current from the annular member to the stationary part.
 9. Awind turbine lightning protection means according to claim 8, where theslip means are a number of metal brushes abutting the annular member andsliding along the annular member, when the mounting flange is rotatingduring operation of the wind turbine.
 10. A wind turbine lightningprotection means according to claim 9, where the slip means being anumber of metal brushes abutting the annular member and sliding alongthe annular member, is secured to the stationary part of the windturbine.
 11. A wind turbine lightning protection means according toclaim 8, where the slip means are a number of carbon brushes abuttingthe annular member and sliding along the member, when the mountingflange is rotating during operation of the wind turbine.
 12. A windturbine lightning protection means according to claim 11, where the slipmeans being a number of carbon brushes abutting the annular member andsliding along the annular member, is secured to the stationary part ofthe wind turbine.
 13. A wind turbine lightning protection meansaccording to claim 8, where the slip means are a number of spatial gaps,said gaps constituting spark gaps for the electrical current to pass inthe form of sparks from the annular member.
 14. A wind turbine lightningprotection means according to claim 13, where the slip means being anumber of gaps is established between the annular member and a number oflightning current receptors, said receptors being is secured to thestationary part of the wind turbine.
 15. A wind turbine lightningprotection system according to claim 8, where the receptors isconstituted by a pointed end neighboring a surface of the annular membersubstantially lying in a plane perpendicular to a rotating axis of themain shaft.
 16. A wind turbine lightning protection system according toclaim 13, where the receptors is constituted by a pointed endneighboring an inner circumference of the annular member, saidcircumference surrounding the rotating axis of the main shaft.
 17. Awind turbine lightning protection system according to claim 13, wherethe receptors is constituted by a pointed end neighboring an outercircumference of the annular member, said circumference surrounding therotating axis of the main shaft.
 18. A wind turbine lightning protectionsystem according to claim 14, where a radial distance in relation to therotating axis of the main shaft between the annular member and thepointed end of each of the lightning current receptors is smaller thanan axial distance in relation to the rotating axis of the main shaftbetween the annular member and the remainder of each of the lightningcurrent receptors.
 19. A wind turbine lightning protection systemaccording to claim 14, where an axial distance in relation to therotating axis of the main shaft between the annular member and thepointed end of each of the lightning current receptors is smaller than aradial distance in relation to the rotating axis of the main shaftbetween the annular member and the remainder of each of the lightningcurrent receptors.
 20. A wind turbine lightning protection systemaccording to claim 19, where the pointed tip of the lightning currentreceptor is cylindrically shaped with the pointed end of the cylindricalshape being directed towards the annular member.
 21. A wind turbinelightning protection system according to claim 14, where the pointed tipof the lightning current receptor is conically shaped with the pointedend of the conical shape being directed towards the annular member. 22.A wind turbine lightning protection system according to claim 14, wherethe pointed tip of the lightning current receptor is frusto-conicallyshaped with the pointed end of the frusto-conical shape being directedtowards the annular member.
 23. A wind turbine lightning protectionsystem according to claim 14, where the pointed tip of the lightningcurrent receptor is pyramidally shaped with the pointed end of thepyramidal shape being directed towards the annular member.
 24. A windturbine lightning protection system according to claim 14, where thepointed tip of the lightning current receptor is triangularly shapedwith the pointed end of the triangular shape being directed towards theannular member.
 25. A wind turbine lightning protection system accordingto claim 14, where the pointed tip of the lightning current receptor isshaped like a fork with a number of prongs with the pointed end of thenumber of prongs being directed towards the annular member.
 26. A windturbine lightning protection means according to claim 7, where theannular member is attached to the stationary part of the wind turbine,thus not rotating with the mounting flange, the main shaft and the hubduring operation of the wind turbine, and where slip means are providedbetween the annular member and the mounting flange, said slip meansconducting the electrical current from the mounting flange to theannular member.
 27. A wind turbine lightning protection means accordingto claim 26, where the slip means are a number of metal brushes abuttingthe annular member and sliding along the annular member, when themounting flange is rotating during operation of the wind turbine.
 28. Awind turbine lightning protection means according to claim 26, where theslip means being a number of metal brushes abutting the annular memberand sliding along the annular member, is secured to the mounting flange.29. A wind turbine lightning protection means according to claim 27,where the slip means being a number of metal brushes abutting theannular member and sliding along the annular member, is secured to themounting flange.
 30. A wind turbine lightning protection means accordingto claim 26, where the slip means are a number of carbon brushesabutting the annular member and sliding along the member, when themounting flange is rotating during operation of the wind turbine.
 31. Awind turbine lightning protection means according to claim 30, where theslip means being a number of carbon brushes abutting the annular memberand sliding along the annular member, is secured to the mounting flange.32. A wind turbine lightning protection means according to claim 26,where the slip means are a number of spatial gaps, said gapsconstituting spark gaps for the electrical current to pass in the formof sparks from the annular member.
 33. A wind turbine lightningprotection means according to claim 32, where the slip means being anumber of gaps is established between the annular member and a number oflightning current receptors, said receptors being secured to themounting flange.
 34. A wind turbine lightning protection systemaccording to claim 32, where the receptors is constituted by a pointedend neighboring a surface of the annular member substantially lying in aplane perpendicular to a rotating axis of the main shaft.
 35. A windturbine lightning protection system according to claim 32, where thereceptors is constituted by a pointed end neighboring an innercircumference of the annular member, said circumference surrounding therotating axis of the main shaft.
 36. A wind turbine lightning protectionsystem according to claim 32, where the receptors is constituted by apointed end neighboring an outer circumference of the annular member,said circumference surrounding the rotating axis of the main shaft. 37.A wind turbine lightning protection system according to claim 32, wherea radial distance in relation to the rotating axis of the main shaftbetween the annular member and the pointed end of each of the lightningcurrent receptors is smaller than an axial distance in relation to therotating axis of the main shaft between the annular member and theremainder of each of the lightning current receptors.
 38. A wind turbinelightning protection system according to claim 32, where an axialdistance in relation to the rotating axis of the main shaft between theannular member and the pointed end of each of the lightning currentreceptors is smaller than a radial distance in relation to the rotatingaxis of the main shaft between the annular member and the remainder ofeach of the lightning current receptors.
 39. A wind turbine lightningprotection system according to claim 32, where the pointed tip of thelightning current receptor is cylindrically shaped with the pointed endof the cylindrical shape being directed towards the annular member. 40.A wind turbine lightning protection system according to claim 32, wherethe pointed tip of the lightning current receptor is conically shapedwith the pointed end of the conical shape being directed towards theannular member.
 41. A wind turbine lightning protection system accordingto claim 32, where the pointed tip of the lightning current receptor isfrusto-conically shaped with the pointed end of the frusto-conical shapebeing directed towards the annular member.
 42. A wind turbine lightningprotection system according to claim 32, where the pointed tip of thelightning current receptor is pyramidally shaped with the pointed end ofthe pyramidal shape being directed towards the annular member.
 43. Awind turbine lightning protection system according to claim 32, wherethe pointed tip of the lightning current receptor is triangularly shapedwith the pointed end of the triangular shape being directed towards theannular member.
 44. A wind turbine lightning protection system accordingto claim 32, where the pointed tip of the lightning current receptor isshaped like a fork with a number of prongs with the pointed end of thenumber of prongs being directed towards the annular member.
 45. A windturbine lightning protection means according to claim 32, where theannular member is attached to the stationary part of the wind turbine,thus not rotating with the mounting flange, the main shaft and the hubduring operation of the wind turbine, and where slip means are providedbetween the annular member and the mounting flange, said slip meansconducting any static electricity, being formed apart from theelectrical current of the lightning, from the mounting flange to theannular member.
 46. A wind turbine lightning protection means accordingto claim 45, where the slip means are a number of metal brushes abuttingthe annular member and sliding along the annular member, when themounting flange is rotating during operation of the wind turbine.
 47. Awind turbine lightning protection means according to claim 46, where theslip means being a number of metal brushes abutting the annular memberand sliding along the annular member, is secured to the stationary partof the wind turbine.
 48. A wind turbine lightning protection meansaccording to claim 47, where the slip means being a number of metalbrushes abutting the annular member and sliding along the annularmember, is secured to the mounting flange.
 49. A wind turbine lightningprotection means according to claim 46, where the slip means are anumber of carbon brushes abutting the annular member and sliding alongthe member, when the mounting flange is rotating during operation of thewind turbine.
 50. A wind turbine lightning protection means according toclaim 46, where the slip means being a number of carbon brushes abuttingthe annular member and sliding along the annular member, is secured tothe stationary part of the wind turbine.
 51. A wind turbine lightningprotection means according to claim 50, where the slip means being anumber of carbon brushes abutting the annular member and sliding alongthe annular member, is secured to the mounting flange.
 52. A windturbine lightning protection means according to claim 46, where the slipmeans are a number of spatial gaps, said gaps constituting spark gapsfor the static electricity to pass in the form of sparks from theannular member.
 53. A wind turbine lightning protection means accordingto claim 46, where the slip means being a number of gaps is establishedbetween the annular member and a number of static discharge units, saidunits being is secured to the stationary part of the wind turbine.
 54. Awind turbine lightning protection means according to claim 46, where theslip means being a number of gaps is established between the annularmember and a number of static discharge units, said units being securedto the mounting flange.
 55. Method for conducting electrical currentinduced by lightning from the blades of a wind turbine to a stationarypart of the wind turbine in relation to a mounting flange of the windturbine, said method comprising passing the electrical current alongelectrical conductors and past the mounting flange from a front side ofthe mounting flange to a rear side of the mounting flange and past thecircumference of the mounting flange.
 56. Method for conductingelectrical current induced by lightning from the blades of a windturbine to a stationary part of the wind turbine in relation to amounting flange of the wind turbine, said method comprising passing theelectrical current along electrical conductors through the mountingflange from a front side of the mounting flange to a rear side of themounting flange.
 57. A mounting flange for mounting the hub to a mainshaft of a wind turbine for conducting electrical current, induced by alightning, along electrical conductors extending from the blades of thewind turbine through the hub, where the mounting flange comprisesfastening means provided in or attached to the circumference of themounted flange for fastening the electrically conducting means to thecircumference of the mounting flange, or through-going holes for passingthe electrically conducting means through, and an annular member ornumber of static discharge units connected to the electrical conductorsand for discharging the electric current to a stationary part of thewind turbine.